Gastrointestinal stromal tumors (GIST/GIPACT) are the most common mesenchymal tumors of the human gastrointestinal (GI) tract and are characterized by the constant immunohistochemical expression of CD117. In recent years, sporadic and germ line mutations in the c-kit gene have been described in GIST/GIPACT tumors, resulting in a constitutive activation of the gene. The most prevalent mutation is located in exon 11 of the c-kit gene, involved in the transcription of the juxta-membrane domain of the c-kit protein. There are conflicting reports with respect to the association between exon 11 mutations and the biological behavior of GIST/GIPACT tumors. This work studies eight patients with tumors diagnosed as GIST/GIPACT, both morphologically and immunohistochemically for CD117, CD34, a-smooth muscle actin, desmin and S-100 protein primary antibodies. The DNA of the eight cases was also studied by PCR for mutation of exon 11 of the c-kit gene. All cases were CD117 positive, but only two showed mutation of exon 11. These last two cases did not show morphological characteristics of malignancy. The most aggressive case, with early death of the patient, did not show the mutation. In conclusion, there was no correlation between the mutation of exon 11 of the c-kit gene and the malignant behavior of GIST/GIPACT tumors in our series.